The central role of the P2Y₁₂ receptor in platelet activation. Exposure of platelets to vWF and collagen results in the adhesion of platelets and subsequent release of ADP from dense granules. Similarly, activation of platelets by thrombin or thromboxane A₂ also results in release of ADP. Secreted ADP activates the P2Y₁₂ receptor (as depicted) and the P2Y₁ receptor (not shown). P2Y₁₂ receptor activation likely affects thrombus growth and stability by recruiting platelets to the site of injury, and by potentiating dense granule release, procoagulant activity, and aggregation.